The present invention relates to a photoconductor for electrophotography (hereinafter referred to as a "photoconductor") for use in electrophotographic apparatuses, such as printers, copying machines and facsimiles. More particularly, the present invention relates to a stable photoconductor having an improved photoconductive layer. The present invention relates also to a method of manufacturing the photoconductor of the present invention.
It is necessary for photoconductors to retain surface charges in the dark, to generate electric charges in response to received light, and to transport the generated electric charges in response to the received light. Photoconductors may be classified into monolayered photoconductors, which have a layer that exhibits all the above described functions, and laminate-type photoconductors, which have a layer for charge generation and another layer for charge transport.
Conventional photoconductors employ the Carlson method for electrophotographic image formation. Image formation by the Carlson method includes the steps of charging the photoconductor in the dark by corona-discharge, forming electrostatic latent images of the original letters and pictures on the charged surface of the photoconductor, developing the electrostatic latent images with toner, and transferring the developed toner images to the carrier paper. The photoconductor is ready to be used again after steps of discharge, removal of residual toner and optical discharge are completed.
Photoconductive materials used in manufacturing conventional photoconductors may include inorganic materials, such as selenium, selenium alloys, zinc oxide, and cadmium sulfide. Photoconductive materials for conventional photoconductors may also include organic photoconductive materials, such as poly-N-vinylcarbazole, 9,10-anthracenediol-polyester, hydrazone, stilbenebutadiene, benzidine, phthalocyanine compounds, and bisazo compounds. The photoconductive materials are often dispersed in a resin binder. Alternatively, the photoconductive materials may be deposited by vacuum deposition or by sublimation.
To obtain a clear image and to facilitate industrial production, it is important for the photoconductor to be of a sufficient sensitivity and to retain surface charges in the dark, i.e. to exhibit a high charge-retention rate. Furthermore, deviations in the charge retention rate must be confined within a narrow range. To improve these electrophotographic properties, the charge generation pigment is often used in an activation-treated form.
Recently, interest in the use of titanyloxyphthalocyanine-containing photoconductive materials has increased, due to their high sensitivity in the long-wavelength region of 700 nm or longer and possibility of favorable application to semiconductor laser-beam printers. The Japanese Unexamined Laid Open Patent Application No. H05-313389 discloses an additive-containing titanyloxyphthalocyanine which exhibits a maximal peak at 27.2 degrees of Bragg angle (2 .theta..+-.0.2.degree.) in an X-ray diffraction spectrum measured with Cu-K .alpha. radiation. The titanyloxyphthalocyanine pigments are also applied in the activation-treated form. The electrophotographic properties of the photoconductors which employ titanyloxyphthalocyanine pigments are further improved by modification of the crystal form of the pigment, such as by an acid pasting treatment or by an appropriate milling treatment.
Although the photosensitivity of the additive-containing titanyloxyphthalocyanine pigment is improved by the treatments as described above, deviations in the charge retention rate often occur. As a result, image defects, including background fogging, are commonly observed.
The cause of the deviations in the charge retention rate is not known. The Japanese Unexamined Laid Open Patent Application No. H03-54572 discloses a substance that is involved in the production of deviations in charge retention rates in metal-free phthalocyanine-containing photoconductors. However, the inter-molecular distance of titanyloxyphthalocyanine is different from that of metal-free phthalocyanine. Moreover, the titanium metal and oxygen in titanyloxyphthalocyanine cause effects which metal-free phthalocyanine does not exhibit. Therefore, the reasons for deviations in the charge retention rate of titanyloxyphthalocyanine pigments remains unknown.